diff --git a/projects/ad7606x_fmc/zed/system_constr.xdc b/projects/ad7606x_fmc/zed/system_constr.xdc
index c7275c3cd..03b553be9 100644
--- a/projects/ad7606x_fmc/zed/system_constr.xdc
+++ b/projects/ad7606x_fmc/zed/system_constr.xdc
@@ -32,3 +32,5 @@ set_property -dict {PACKAGE_PIN P17     IOSTANDARD LVCMOS25} [get_ports adc_os[1
 set_property -dict {PACKAGE_PIN N17     IOSTANDARD LVCMOS25} [get_ports adc_os[2]]          ; ## H16 FMC_LPC_LA11_P
 set_property -dict {PACKAGE_PIN T19     IOSTANDARD LVCMOS25} [get_ports adc_stby]           ; ## C15 FMC_LPC_LA10_N
 set_property -dict {PACKAGE_PIN R21     IOSTANDARD LVCMOS25} [get_ports adc_range]          ; ## D15 FMC_LPC_LA09_N
+set_property -dict {PACKAGE_PIN K19     IOSTANDARD LVCMOS25} [get_ports adc_serpar]         ; ## C18 FMC_LPC_LA14_P
+set_property -dict {PACKAGE_PIN K20     IOSTANDARD LVCMOS25} [get_ports adc_refsel]         ; ## C19 FMC_LPC_LA14_N
diff --git a/projects/ad7606x_fmc/zed/system_top.v b/projects/ad7606x_fmc/zed/system_top.v
index 7ef1b3e21..717d2c6b0 100644
--- a/projects/ad7606x_fmc/zed/system_top.v
+++ b/projects/ad7606x_fmc/zed/system_top.v
@@ -94,7 +94,9 @@ module system_top (
   output                  adc_reset,
   output      [2:0]       adc_os,
   output                  adc_stby,
-  output                  adc_range
+  output                  adc_range,
+  output                  adc_refsel,
+  output                  adc_serpar
 );
 
   // internal signals
@@ -117,18 +119,13 @@ module system_top (
 
   // instantiations
 
-  ad_iobuf #(
-    .DATA_WIDTH(6)
-  ) i_iobuf_adc_cntrl (
-    .dio_t (gpio_t[37:32]),
-    .dio_i (gpio_o[37:32]),
-    .dio_o (gpio_i[37:32]),
-    .dio_p ({adc_reset,        // 37
-             adc_stby,         // 36
-             adc_range,        // 35
-             adc_os}));        // 34:32
-
-  assign gpio_i[63:38] = gpio_o[63:38];
+  assign adc_serpar = gpio_o[39];
+  assign adc_refsel = gpio_o[38];
+  assign adc_reset = gpio_o[37];
+  assign adc_stby = gpio_o[36];
+  assign adc_range = gpio_o[35];
+  assign adc_os = gpio_o[34:32];
+  assign gpio_i[63:32] = gpio_o[63:32];
 
   generate
     for (i = 0; i < 16; i = i + 1) begin: adc_db_io